1. Field of the Invention
The present invention relates to a bar-shaped semiconductor laser chip comprising a nitride semiconductor substrate, and to a method for fabricating such a semiconductor laser chip.
2. Description of Related Art
There have conventionally been known semiconductor laser chips comprising a nitride semiconductor substrate. For example, one such semiconductor laser chip is disclosed in JP-A-2008-205171.
JP-A-2008-205171 mentioned above discloses a nitride semiconductor laser chip which comprises: a substrate formed of a nitride semiconductor; an n-side semiconductor layer, an active layer, a p-side semiconductor layer, and a p-electrode formed on the main (obverse) surface of the substrate; and an n-electrode formed on the back (reverse) surface of the substrate.
In this nitride semiconductor laser chip, the resonator (cavity) facets lie on the (1-100) plane. That is, the resonator facets are formed so as to extend in the [11-20] direction.
On the other hand, there have conventionally been known bar-shaped semiconductor laser chips comprising a nitride semiconductor substrate. A bar-shaped semiconductor laser chip is formed by arraying a plurality of laser chip portions in a predetermined direction.
When such a bar-shaped semiconductor laser chip is formed by use of, for example, the nitride semiconductor laser chip disclosed in JP-A-2008-205171 mentioned above, the bar-shaped semiconductor laser chip is formed so as to extend in the [11-20] direction. That is, the bar-shaped semiconductor laser chip is formed in the shape of a bar having laser chip portions (individual nitride semiconductor laser chips) arrayed in the [11-20] direction.
Inconveniently, however, since the off-angle of the nitride semiconductor substrate is not uniform over its surface, in a bar-shaped semiconductor laser chip, the off-angle of the nitride semiconductor substrate varies among the individual laser chip portions. Thus, in a case where, as in the bar-shaped semiconductor laser chip mentioned above, the laser chip portions (individual nitride semiconductor laser chips) are arrayed in the [11-20] direction, their oscillation wavelength (lasing wavelength) gradually increases (or decreases) in the [11-20] direction. This brings the problem of a large difference between the oscillation wavelength of the endmost laser chip portion in the [11-20] direction and the oscillation wavelength of the endmost laser chip portion in the [−1-120] direction, which is to say the problem that the bar-shaped semiconductor laser chip suffers from a large variation in oscillation wavelength.
A bar-shaped semiconductor laser chip with a large variation in oscillation wavelength is disadvantageous because it, for example when used as a light source in an exposure machine, makes uniform exposure difficult.